Background chromakey panels are commonly used in the art of television and video production in order to facilitate merging of a virtual background with foreground figures. The foreground figures are imaged on the chromakey panel background, and the known color of the chromakey panel background is detected and replaced by the virtual background. One problem associated with such productions is that changes in the foreground image, due to camera displacement, pan, tilt and zoom in and out, are not automatically applied to the background scene.
One system designed to solve this problem is the "Virtual Studio" developed by Ultimatte. The "Virtual Studio" requires a special memory head pedestal which measures the camera's pan and tilt angles directly from the camera's mount. A disadvantage of this approach is that in order to obtain a complete perspective transformation for the background image, the zoom state of the lens must be read and the instantaneous location of the camera must be determined. Also, this approach requires that each and every camera mount be replaced by a memory head pedestal, resulting in an expensive system and complicated operation if a large number of cameras are employed. Also, the accuracy of this method is inadequate for seamless foreground/background merging.
Conventional edge detection methods which are based on smoothing and finding directional derivates are described in the following publication, the disclosure of which is hereby incorporated by reference:
Canny, J., "A computational approach to edge detection", IEEE Trans. on PAMI, PAMI-8, No. 6, 1986, 679-697.
Conventional edge detection methods which are based on Hough transforms are surveyed in the following publication, the disclosure of which is hereby incorporated by reference:
J. Illingworth and J. Kitler, "A survey of the Hough transform", CVGIP, 44, 1988, 87-116.
FIG. 1A is a simplified block diagram of a state of the art chromakeying system.